At least nine people have died after the massive eruption of Mount St Helens volcano in Washington State, USA.

Many more are missing and the death toll is expected to rise.

A huge cloud of ash has turned day into night for towns and cities across north-western America. People have been told to stay indoors and wear gauze masks. Many roads have been closed, trains halted and aircraft grounded.

Mount St Helens exploded at 0832 local time on 18 May.

Avalanches of hot ash

It triggered an earthquake measuring 5.2 on the Richter scale and the north face of the mountain collapsed in a massive avalanche.

At the same time a giant mushroom-shaped cloud of ash rose 15 miles (24km) into the sky in just 15 minutes. Then avalanches of hot ash, pumice and gas known as pyroclastic flows poured out of the crater.

Westerly winds have blown millions of tons of ash across the United States turning blue skies grey as far as Spokane, Washington - 250 miles (400km) away.

Nearly 150 square miles (240 sq km) of forest has been destroyed and it is believed thousands of wild animals have been killed.

One of those who died was local celebrity 84-year-old Harry Truman. The former president's namesake had consistently refused to leave his motel at the foot of the mountain beside Spirit Lake.

He stayed with his 16 cats and 18 racoons while about 2,000 people were evacuated from the area in the last few weeks as the mountain threatened to blow.

The lake has been wiped out by the massive force of the eruption along with boiling mud flows triggered by mountain snow that melted in the intense heat.

Dr Bob Christiansen of the US Geological Survey who predicted the huge eruption said another major blast was unlikely.

The explosion had the power of 500 atomic bombs and was the largest of its kind in recorded US history.

The final number of those who died directly from the eruption was 57. The Washington State Department of Game estimated nearly 7,000 big game animals (deer, elk, and bear) perished as well as all birds and most small mammals.

Of the 32 species of small mammals thought to be living near Mount St Helens only 14 were known to have survived, according to the US Department of Agriculture.

Scientists learned a great deal about volcanos from the explosion and have been studying how plant life has gradually returned to the once devastated region around the mountain.

The volcano became active again in October 2004 but scientists believe the chances of an imminent eruption as huge as that of 1980 are low.